Ideally, TCP/IP is used whenever Windows-based computers communicate over networks. The TCP/IP protocol is actually made up of several different protocols that interoperate to provide the functionality we expect from our networks and the Internet. There are a great many resources out there to help you learn more about TCP/IP.
We’re all aware that the Internet depends on the functions of the TCP/IP (Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)) protocol. That’s when the International Standards Organization (ISO) designed the Open System Interconnection (OSI) model to serve as a guideline for independent vendors building communications platforms for computers (networks). The OSI model broke the sequence of networking computers into these seven basic parts:
Application
Presentation
Session
Transport
Network
Data link
Physical
Each part (or layer) performed specific functions and then passed on the necessary information to the layer above or below (according to how the information was flowing). Whether information packets were moving up the model or down, each layer had to perform its function while communicating with the surrounding layers.
Enter the super protocol (TCP/IP)
When TCP/IP arrived on the scene, it had to conform to the seven layers in the OSI model, but it made things easier on everyone by combining them into the following layers:
Application layer
Transport layer
Internet layer
Network access layer (Subnet)
The following figure shows comparison and relationships of IOS and TCP/IP.
As you can see, TCP/IP integrated the functions of the Application, Presentation, and Session layers into a more practical Application layer that contains many of the basic applications we now take for granted on the Internet.
The Network layer was basically renamed to reflect the Internet capabilities of the entire protocol stack and the Data link and Physical layers’ functionality combined into the Network access or Subnet layer. That left the Transport layer, which uses the TCP and UDP protocols, depending on the type of application being run.
Dissecting the Transport layer
As shown in the above figure, the Transport layer of the TCP/IP protocol stack is made up of the TCP and UDP protocols. According to the type of application you’re running and the demands it makes on your network, you’ll use one or the other and in some cases, both. No matter which one you use, they are both dependent on the Internet layer and its Internet Protocol (IP) to communicate across packet-switched networks. Now, let’s share details of UDP and TCP in details.
UDP
This means that the applications can’t really depend on IP to get their packets to the receiving computer or to do it in the right order, if that’s important. That’s where TCP and UDP start to perform their magic. UDP takes advantage of IP to establish the proper route for the data it’s sending to the receiving computer. UDP is also a connectionless protocol and doesn’t ensure data integrity, provide for error correction, or seek an acknowledgement of receipt as it sends packets out across the network. It just sends the data as fast as the available bandwidth will allow. This makes it especially effective for Domain Name Service (DNS) and Network File System (NFS) applications, which depend on fast responses to client requests for data.
TCP
If the application requires that the packets arrive in a certain order or considers every packet sent valuable, then the TCP protocol will be employed to ensure delivery. TCP is a connection-oriented protocol that inspects each packet sent across the network and also guarantees the integrity of each and every packet and its encapsulated data. Basically, the TCP protocol establishes a two-way stream of information between computers and waits for a response from the receiving computer before sending out the next sequenced packet of data. Once the data is completely sent and positively received, it closes the stream.
